This disclosure relates generally to optical devices, and more particularly, but not exclusively, to tunable wavelength converters utilizing a Bragg grating and a laser in a semiconductor substrate.
With the continued growth of the Internet and multimedia communications, the demand for increased capacity on networks has fueled the evolution and use of optical fibers. In an effort to optimize the data carrying capacity of optical fiber networks, dense wavelength-division multiplexing (xe2x80x9cDWDMxe2x80x9d) systems and the like have been implemented to carry data via a plurality of wavelengths (i.e., channels) within a single fiber.
In a high-speed optical network, wavelength conversion, in which information is optically transformed from one wavelength to another will perform an important function. For instance, one may appreciate that in a large-scale optical network, as the density of traffic increases, the network may have many vacant channels on all of its links, but a single unique wavelength may be unavailable on any possible path between two end users. As such, it will be necessary to change the wavelength of some signals as they traverse the network in order to accommodate multiple users in the most efficient manner.
One straightforward solution to wavelength conversion is to simply convert a received optical signal to electronic form, and then re-transmit a second optical signal at the desired wavelength. However, the optical-electronic-optical conversion process is relatively slow, and limits the efficiency and speed of the optical network. Current types of fully optical wavelength converters utilize the non-linear optical properties of a semiconductor optical amplifier (xe2x80x9cSOAxe2x80x9d), such as cross-gain modulation, cross-phase modulation, and four-wave mixing. While these processes are more efficient than optical-electronic-optical conversions, the wavelength conversion speed of these processes is fundamentally limited by the carrier dynamics in the SOA. For example, the optical properties of the SOA are determined, at least in part, by carrier interband transitions that involve relatively slow processes such as Auger processes.
Commonly used optical components in DWDM systems include wavelength-division multiplexing transmitters and receivers, optical filters such as diffraction gratings, thin-film filters, fiber Bragg gratings, arrayed-waveguide gratings, optical add/drop multiplexers, and tunable lasers. For instance, lasers are well known devices that emit light through stimulated emission and produce coherent light beams with a frequency spectrum ranging from infrared to ultraviolet, and may be used in a vast array of applications. For example, in optical communication or networking applications, semiconductor lasers may be used to produce light or optical beams on which data or other information may be encoded and transmitted.
Other devices used in optical communication or networking applications are fiber-based Bragg gratings. A fiber Bragg grating is an optical fiber device that includes an optical fiber with periodic changes in the refractive index of fiber core materials along the fiber length, which may be formed by exposure of the photosensitive core to an intense optical interference pattern. With the changes in the refractive index along the fiber length, optical beams at a particular wavelength are reflected by the fiber Bragg grating while other wavelengths are allowed to propagate through the fiber.
One limitation of fiber Bragg gratings is that the particular wavelength that is reflected by the fiber Bragg grating is substantially fixed. Consequently, if different wavelengths of light are to be reflected, different fiber Bragg gratings are utilized. In some known fiber Bragg gratings, nominal adjustments to the reflected wavelength may be provided by physically or mechanically stretching the optical fiber of the fiber Bragg grating to modify the length of the optical fiber. The disadvantage of this technique is that the amount of adjustment to the reflected wavelength is relatively small and the optical fiber may suffer damage from the physical stress and strain of the stretching.